1. Field of the Invention
The present invention relates to a method of manufacturing an optical component, particularly, to a method of manufacturing a waveguide type optical component used in the field of an optical communication.
2. Description of the Related Art
In general, a waveguide type optical component is considered to play a vital role in the future in the field of an optical communication. In particular, a waveguide type optical component using a silica-based material exhibits an excellent compatibility with an optical fiber and, thus, is expected to create a big demand.
A folding or bending type optical waveguide having a mirror housed therein as shown in FIGS. 1 and 2 is known to the art as a waveguide type optical component using a silica-based material. Specifically, FIG. 1 is a plan view showing the folding or bending type optical waveguide noted above, with FIG. 2 showing a cross section along the line 2--2 shown in FIG. 1. A folding or bending type optical waveguide of this type is manufactured as follows.
In the first step, a lower cladding layer 12 consisting of a silica-based material and a core layer consisting of a silica-based material containing germanium are formed on a silicon substrate 11 by means of, for example, a flame hydrolysis deposition method, a vacuum evaporation method, a plasma CVD method or a sol-gel method. The lower cladding layer 12 is formed in a thickness of about 20 .mu.m. On the other hand, the core layer is formed in a thickness of about 8 .mu.m. In this case, the refractive index difference between the lower cladding layer 12 and the core layer can be set at, for example, about 0.25%.
In the next step, the core layer is patterned by, for example, a photolithography method with a reactive ion etching method to form a predetermined waveguide core 13 having a pattern width of about 8 .mu.m. After the patterning step, an upper cladding layer 14 is formed in a thickness of about 20 .mu.m as in the formation of the lower cladding layer 12, with the result that the waveguide core 13 is covered with the upper cladding layer 14.
Further, a groove having a depth of about 35 .mu.m and defined by a wall perpendicular to the substrate surface is formed by means of a photolithography method with a reactive ion etching method, followed by depositing a metallic material such as gold having a thickness of about 0.1 .mu.m on the vertical wall surface of the groove by means of, for example, a vacuum evaporation method or a sputtering method so as to form a mirror 16, thereby obtaining a folding or bending type optical waveguide having a mirror housed therein.
In an optical integrated circuit of this type, it is necessary to control very accurately the positional relationship between the optical waveguide and the mirror. Deviation of the mirror position brings about a change in the direction of the propagating lightwave, resulting in failure to guide the lightwave reflected from the mirror to the optical waveguide accurately. It follows that the characteristics of the optical integrated circuit are markedly deteriorated.
It should be noted that the surface of the upper cladding layer 14 is relatively smooth, making it very difficult to detect the position of the optical waveguide on the basis of the surface unevenness. However, where the upper cladding layer 14 is formed of a transparent material such as a silica glass, it is possible to detect the position of the optical waveguide by optically recognizing, for example, the shape of the waveguide core or the position aligning pattern buried in advance in the upper cladding layer 14. In this case, an etching mask, which is used in the step of processing, for example, a mirror, and is formed before the position alignment, is required to be a transparent material. It follows that serious restrictions are required in the manufacturing method and selection of the materials.
where a position aligning pattern is used as it is as a basis of the position alignment in the subsequent processing, it is difficult in general to visually recognize the position aligning pattern depending on the step required for the subsequent processing. In some cases, the visual recognition of the position aligning pattern is rendered impossible. In order to avoid the difficulty, it is made necessary to select a step which does not impair the capability of visually recognizing the position aligning pattern, leading to a serious restriction in the method of manufacturing an optical component.